Last night i was using the octavia and the trip computer was showing 25 miles to empty, i was .5 miles away from a petrol station, so went and finished what i was doing then got back in the car and it showed 15 miles to empty, then 0 and then died. so i had to walk to a petrol station and buy a petrol can and £5 of fuel.

Then drove to the petrol station and put more fuel in. but the needle didn't move up.

then it said 115 miles to empty and the needle ony moved to quarter of a tank. so i drove and dropped of the misses some 15 miles away, by that time the needle had moved to half a tank where it should be.

I also had a similar issue earlier in the day where i had 110 miles to empty, got in the car and it said 5 miles and the needle was on empty.

Could this just be a sticky float, or is it all electronc ?

It might be a sticky float; the available range mode on the computer works off fuel flow and distance covered.